The significance and sources of unesterified and esterified cholesterol in intestinal chylomicrons will be sought using rats with mesenteric lymphatic fistulas, that are receiving emulsified triglyceride by continuous duodenal infusion. Variations in the surface composition and the core to surface component ratios of chylomicrons during prolonged triglyceride transport at high rates in the presence or absence of exogenous phospholipid will be described. Differences in composition will be correlated with chylomicron size determined by electronmicroscopy with negative staining. Studies of intestinal lymph and portal venous lecithin-cholesterol acyl transferase (LCAT) activities and high density lipoprotein (HDL) concentrations will seek to establish that intestinal sources exist for both the enzyme and HDL. Any changes in LCAT activity occurring as a result of intestinal absorption of specific food substances, notably lipid, will be assessed.